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<script>
    // 1、求1 + 2！ + 3！ + 4！....+20!的值
	// - 2！ = 2 * 1
    // - 3！ = 3 * 2 * 1
    var sum=0;
    for(var i=1;i<=20;i++){
        var n=1;
        for(var j=1;j<i+1;j++){
            n=n*j;
        }
        sum=sum+n;
    }
    console.log(sum);





</script>
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